The darkening of skin color is a concern for many individuals. Most people obtain darker skin through exposure to UV light (e.g., suntanning or UV lamps). Production of melanin and the type of melanin when stimulated by UV are genetically determined. UV exposure, however, results in accelerated skin aging and increased incidence of skin cancer. The ability to generate a tanned appearance without incurring photodamage, thus, is important to many individuals. Accordingly, alternative methods for “sunless tanning” have evolved.
One method is the use of products containing dihydroxy acetone (DHA). Some of these products, however, produce color that is too orange and unnatural to the user. Moreover, the DHA-produced skin color only minimally protects the user from UV irradiation. Products containing beta-carotene, cantaxanthin and lycopene have also been used to darken the skin. These products, however, have no effect at all on melanogenesis and usually result in unnatural and uneven distributed skin color by saturating and staining the fat layers just below the skin. In addition, these products do not provide any sun-protection as compared to naturally tanned skin. Melanotan and MelanX are synthetic hormone drugs that mimic the action of melanocyte-stimulating hormone (MSH) and are used to darken the skin only when administered by injection, not orally or topically. Psoralens, on the other hand, work by making the skin hypersensitive to the sun and therefore melanin production is accelerated. They do not make the skin darker without exposure to UV, and that exposure must be carefully regulated to minimize the serious risk for skin cancer. Psoralens in conjunction with medical grade UV lamps are an accepted treatment for people afflicted with vitiligo and psoriasis, but are not recommended for patients with fair skins. Thus, a product is desired that would enhance the body's natural pigment content, resulting in a desired skin color and enhanced photo-protection without the need of UV exposure.
Rhubarb is one of the oldest and well-known Chinese herbal medicines. Rhubarb root has traditionally been used as a laxative, antiphlogistic, and haemostatic in the treatment of constipation, jaundice, gastrointestinal hemorrhage, menstrual disorders, conjunctivitis, traumatic injuries, superficial sores and ulcers. It has also been applied externally for thermal burns. Rhubarb has been reported for the treatment of dermatosis such as atopic dermatitis (see Japanese Patent Nos. 07138173 and 07010733), for being an antioxidant (Japanese Patent Nos. 06025663 and 04005237), and for the cosmetic applications such as melanin formation inhibitor (Japanese Patent No. 2000281528) and improving skin roughness (Japanese Patent No. 2000212059). It has also been reported for the treatment of diabetes (European Patent No. 0941103 and PCT Patent Application No. WO9819688) and for inhibiting binding of 5-dihydro-testosterone with androgen receptors (U.S. Pat. No. 4,987,150).
The present inventors have now unexpectedly discovered that rhubarb is effective for darkening the skin and/or hair.